1. Field of the Invention
The present invention relates to a liquid discharge head for discharging a liquid and a producing method therefor, and more particularly to an electrode pad of a substrate for the liquid discharge head.
2. Description of the Related Art
There is already known a method for producing an ink jet recording head, utilizing a semiconductor manufacturing process and enabling electrical connection of an element substrate without dust deposition, for example in a clean room (Japanese Patent Application Laid-open No. 2005-199701). In this producing method, an electrode pad of the element substrate is formed by an electrolytic plating.
In such producing method, an element substrate is prepared at first, then a gold bump for an electrode pad is formed by an electrolytic plating, and a flow path wall forming member is provided thereafter. In the step of forming the element substrate, a heater, an electrode pad for external connection, and an electrode pad for testing are formed on the substrate. As the gold bump forming step involves a chemical treatment, the flow path wall forming member is to be provided after the gold bump is formed.
The gold bump formation for the electrode pad by electrolytic plating is executed by the following steps in succession, which are an undercoat layer forming step with a high-melting point metal material such as TiW, an Au (undercoat seed gold) film forming step, a resist coating/exposure/developing step, a gold deposition step by an electrolytic plating, a resist stripping step, an etching step for the undercoat seed gold, and an etching step for the undercoat layer of high-melting point metal material.
In the manufacture of an ink jet recording head, in addition to an external connection electrode pad for exchanging electrical signals with the exterior, a test electrode pad to be used as an electrode for testing a circuit formed on the head substrate may also be formed on the substrate. In the above-described manufacturing process, however, in the case that the test electrode pad is not gold plated, the exposed test electrode pad (made of aluminum or an aluminum alloy) may be corroded at the etching of the undercoat seed gold, or of the undercoat layer of high-melting point metal material.
The test electrode pad is therefore plated with gold in order to avoid such erosion.
In the following, a process of gold plating on the test electrode pad will be described with reference to FIGS. 11A and 11B. FIGS. 11A and 11B are schematic views showing intermediate steps in the manufacture of a prior ink jet recording head, wherein FIG. 11A is a perspective view and FIG. 11B is a partial cross-sectional view of a portion 11B-11B.
On an aluminum wiring 10b of the test electrode pad 8, a gold bump 18b is formed, and an adhesive layer 2 utilizing a resinous material is laminated thereon. Then, a flow path wall forming member 3, having an ink flow path therein, is provided so as to cover the upper part thereof with photosensitive resin. The test electrode pad 8, though no longer necessary after the formation of the flow path wall forming member 3, has a structure connectable to the circuit and is in an electrically conductive state during the use of the ink jet recording head. Therefore, the test electrode pad 8 is insulated by the adhesive layer 2. Also on the aluminum wiring 10a of the external connection electrode pad 7, a gold bump 18a is formed, which is connected to an external electrode member 15 and is then sealed by a sealant 16.
In such structure, however, the flow path wall forming member 3 may be partly peeled by a thermal contraction at the manufacture or the insulation by the adhesive layer 2 on the test electrode pad 8 may become insufficient, so that the aluminum wiring 10b may come into contact with the ink and may be corroded. Such corrosion of the aluminum wiring 10b further induces a corrosion spreading to a wiring portion which is satisfactorily insulated.